A comparative study of non-native N-acyl l-homoserine lactone analogs in two Pseudomonas aeruginosa quorum sensing receptors that share a common native ligand yet inversely regulate virulence

Abstract

Certain bacteria can coordinate group behaviors via a chemical communication system known as quorum sensing (QS). Gram-negative bacteria typically use N-acyl l-homoserine lactone (AHL) signals and their cognate intracellular LuxR-type receptors for QS. The opportunistic pathogen Pseudomonas aeruginosa has a relatively complex QS circuit in which two of its LuxR-type receptors, LasR and QscR, are activated by the same natural signal, N-(3-oxo)-dodecanoyl l-homoserine lactone. Intriguingly, once active, LasR activates virulence pathways in P. aeruginosa, while activated QscR can inactivate LasR and thus repress virulence. We have a limited understanding of the structural features of AHLs that engender either agonistic activity in both receptors or receptor-selective activity. Compounds with the latter activity profile could prove especially useful tools to tease out the roles of these two receptors in virulence regulation. A small collection of AHL analogs was assembled and screened in cell-based reporter assays for activity in both LasR and QscR. We identified several structural motifs that bias ligand activation towards each of the two receptors. These findings will inform the development of new synthetic ligands for LasR and QscR with improved potencies and selectivities.

Quorum Sensing Signal Selectivity and the Potential for Interspecies Cross Talk

“…Consistent with previous findings using E. coli reporters (20, 41–43), QscR responded strongly to nonself signals. While QscR was most responsive to N -decanoyl-L-homoserine lactone (C10-HSL), the next most active signals each have a 12-carbon acyl chain.…”

“…To date, classification of QS receptors as “specific” or “promiscuous” has largely been qualitative. Semiquantitative scores have been used to make pairwise comparisons of relative selectivity between receptors (43) or signals (25), but there has yet to be a single score that represents a receptor’s response to every signal. We sought to develop a quantitative score of selectivity such that the receptors could be more robustly compared to one another.…”

“…coli has an AHL receptor, SdiA, which can interfere with receptor activity studies by activating transcription from the target promoter (64, 65). Although some researchers use sdiA deletion strains (43, 66), it is common to use readily available chemically competent cells such as TOP10 or, as we have, DH5α which have intact sdiA and the potential for artifacts associated with this receptor. We note, however, that in our E.…”

Structure–Function Analyses of the N-Butanoyl l-Homoserine Lactone Quorum-Sensing Signal Define Features Critical to Activity in RhlR

“…While thiolactone analogs of other AHLs have been reported to have comparable or lower agonistic activity than their parent AHL (34, 35) , 26 represents to our knowledge the first thiolactone analog that is more potent than the native AHL ligand. We do note that LuxR-type receptor SdiA in Salmonella enterica serovar Typhimurium has been reported to be more strongly activated by ligands bearing thiolactone relative to lactone head groups, but this receptor is an “orphan” type LuxR receptor that lacks a native ligand for direct comparison (36) .…”

Easily Accessible, Highly Potent, Photocontrolled Modulators of Bacterial Communication

“…In the context of QS, earlier work by our group focused on the design of photoswitchable QS autoinducers, which led to the photocontrol of QS-related gene expression and pyocyanin production. 33 This proof of concept, together with an abundance of synthetic QS ligands developed, [34][35][36] has paved the way for the further advancement toward more potent and selective autoinducers that can be controlled with light.…”